1. Technical Field
The present invention relates to methods of production, methods of use, and compositions of small spherical particles of an active agent. In accordance with the method of production, the active agent is dissolved in an aqueous or aqueous-miscible solvent containing a dissolved phase-separation enhancing agent (PSEA) to form a solution in a single liquid phase. The solution is then subjected to a liquid-solid phase separation having the active agent comprising the solid phase and the PSEA and solvent comprising the liquid phase. The liquid-solid phase separation can be induced in numerous ways, such as changing the temperature of the solution to below the phase transition temperature of the system. The method is most suitable for forming small spherical particles of therapeutic agents which can be delivered to a subject in need of the therapeutic agent. The method is also most suitable for forming solid, small spherical particles of macromolecules, particularly macromolecules which are heat labile, such as proteins.
2. Background Art
Several techniques have been used in the past for the manufacture of biopolymer nano- and microparticles. Conventional techniques include spray drying and milling for particle formation and can be used to produce particles of 5 μm or less in size.
U.S. Pat. No. 5,654,010 and U.S. Pat. No. 5,667,808 describe the production of a solid form of recombinant human growth hormone, hGH, through complexation with zinc in order to create an amorphous complex, which is then micronized through an ultrasound nozzle and sprayed down in liquid nitrogen in order to freeze the droplets. The liquid nitrogen is then allowed to evaporate at a temperature of −80° C. and the resultant material is freeze-dried.
Microparticles, microspheres, and microcapsules are solid or semi-solid particles having a diameter of less than one millimeter, more preferably less than 100 microns and most preferably less than 10 microns, which can be formed of a variety of materials, including proteins, synthetic polymers, polysaccharides and combinations thereof. Microspheres have been used in many different applications, primarily separations, diagnostics, and drug delivery.
The most well known examples of microspheres used in separations techniques are those which are formed of polymers of either synthetic or natural origin, such as polyacrylamide, hydroxyapatite or agarose. In the controlled drug delivery area, molecules are often incorporated into or encapsulated within small spherical particles or incorporated into a monolithic matrix for subsequent release. A number of different techniques are routinely used to make these microspheres from synthetic polymers, natural polymers, proteins and polysaccharides, including phase separation, solvent evaporation, coascervation, emulsification, and spray drying. Generally the polymers form the supporting structure of these microspheres, and the drug of interest is incorporated into the polymer structure.
Particles prepared using lipids to encapsulate target drugs are currently available. Liposomes are spherical particles composed of a single or multiple phospholipid and/or cholesterol bilayers. Liposomes are 100 nanometer or greater in size and may carry a variety of water-soluble or lipid-soluble drugs. For example, lipids arranged in bilayer membranes surrounding multiple aqueous compartments to form particles may be used to encapsulate water soluble drugs for subsequent delivery as described in U.S. Pat. No. 5,422,120 to Sinil Kim.
Spherical beads have been commercially available as a tool for biochemists for many years. For example, antibodies conjugated to beads create relatively large particles that have binding specificity for particular ligands. Antibodies are routinely used to bind to receptors on the surface of a cell for cellular activation, are bound to a solid phase to form antibody-coated particles for immunoaffinity purification, and may be used to deliver a therapeutic agent that is slowly released over time, using tissue or tumor-specific antibodies conjugated to the particles to target the agent to the desired site.
There is an on-going need for development of new methods for making particles, particularly those that can be adapted for use in the drug delivery, separations and diagnostic areas. The most desirable particles from a utility standpoint would be small spherical particles that have the following characteristics: narrow size distribution, substantially spherical, substantially consisting of only the active agent, retention of the biochemical integrity and of the biological activity of the active agent. The particles should provide a suitable solid that would allow additional stabilization of the particles by coating or by microencapsulation. Further, the method of fabrication of the small spherical particles would have the following desirable characteristics: simple fabrication, an essentially aqueous process, high yield, and requiring no subsequent sieving.